Recent studies by ourselves and others have substantially elucidated the role of the HIV-1 encoded viral infectivity factor (Vif) in neutralizing a potent antiviral system that occurs in lymphocytes and macrophages and some leukemic T cell lines. This antiviral system principally involves the cytidine deaminases APOBEC3G (A3G) and/or ASF, which are incorporated into HIV-1 cores where they lethally hypermutate newly synthesized viral reverse transcripts. Vif binds to A3G and ASF and.induces their polyubiquitination and degradation, thereby eliminating them from infected cells and precluding their incorporation into HIV-1 progeny. Although researchers have used one Vif as a standard, HIV-1 Vifs are highly divergent and we have found that natural HIV-1 isolates encode Vifs that bind promiscuously to all APOBEC3 paralogs but have widely distinctive effects on their concentrations. In addition, the APOBECSs are coexpressed in different amounts and proportions in HIV-1 susceptible cells, and they broadly heterooligomerize to form a collaborative and inducible antiviral network. Our results suggest that Vif diversity is partly an adaptive response to the diversity of the APOBEC3 network in different cells and compartments, that it may play a critical role in HIV-1 pathogenesis, and that it should also be considered in anti-Vif drug development. Based on these results and on substantial preliminary evidence, we propose three substantial and synergistic aims: (1) Develop a robust series of screening platforms for identification of small molecules that inhibit diverse Vifs within mammalian cells. (2) We found that HIV-1 Vif is made in yeast as a soluble protein that associates with A3G. Produce substantial amounts of Vif, and its A3G-binding subdomain and A3G in the yeast Pichia pastorisas a resource to analyze inhibitor mechanisms, and to support the high throughput screening system of aim 3. (3) Optimize ELISA assays to screen and analyze compounds that inhibit Vif- A3G binding and to measure affinities of diverse Vifs for A3G and other cytidine deaminases. This program builds on recent insights to develop and to optimize novel inhibitor screening approaches and investigational resources for AIDS, as an essential prelude to high throughput screening for effective anti-Vif therapeutics.